Rewrite spacing commands as macros (#1156)

* Rewrite spacing commands as macros

Fix #1130 by defining `\!`, `\negthinspace`, `\,`, `\thinspace`, `\:`,
`\medspace`, `\;`, `\thickspace`, `\negmedspace`, `\negthickspace`,
`\enspace`, `\enskip`, `\qquad`, `\quad` as macros.

Fix #1036 by defining a new `SpaceNode` in mathMLTree that recognizes
all special space amounts from
https://www.w3.org/TR/2000/WD-MathML2-20000328/chapter6.html

* Fix <mspace> rendering and add a test to catch it

* Update screenshots

* Wrap special space characters in <mtext>

* Update screenshots

* Fix MathML escaping behavior

* Fix flow typos

* Fix Unicode-chrome

* Reimplement mod operators in terms of macros

* Rerun ModScript

* Remove excess table entries (now already macros)

* Fix bmod

test/__snapshots__/mathml-spec.js.snap

@@ -57,6 +57,24 @@ exports[`A MathML builder accents turn into <mover accent="true"> in MathML 1`]
 
 `;
 
+exports[`A MathML builder normal spaces render normally 1`] = `
+
+<math>
+  <semantics>
+    <mrow>
+      <mspace width="1em">
+      </mspace>
+      <mspace width="0.431em">
+      </mspace>
+    </mrow>
+    <annotation encoding="application/x-tex">
+      \\kern1em\\kern1ex
+    </annotation>
+  </semantics>
+</math>
+
+`;
+
 exports[`A MathML builder should concatenate digits into single <mn> 1`] = `
 
 <math>
@@ -125,8 +143,9 @@ exports[`A MathML builder should generate the right types of nodes 1`] = `
       <mn>
         1
       </mn>
-      <mspace width="0.277778em">
-      </mspace>
+      <mtext>
+        &ThickSpace;
+      </mtext>
       <mtext>
         a
       </mtext>
@@ -169,7 +188,7 @@ exports[`A MathML builder should output \\limsup_{x \\rightarrow \\infty} correc
       <msub>
         <mo>
           <mi mathvariant="normal">
-            lim sup
+            lim&ThinSpace;sup
           </mi>
           <mo>
             ⁡
@@ -204,7 +223,7 @@ exports[`A MathML builder should output \\limsup_{x \\rightarrow \\infty} in dis
       <munder>
         <mo>
           <mi mathvariant="normal">
-            lim sup
+            lim&ThinSpace;sup
           </mi>
           <mo>
             ⁡
@@ -519,6 +538,74 @@ exports[`A MathML builder should use <munderover> for large operators 1`] = `
 
 `;
 
+exports[`A MathML builder special spaces render specially 1`] = `
+
+<math>
+  <semantics>
+    <mrow>
+      <mtext>
+        &ThinSpace;
+      </mtext>
+      <mtext>
+        &ThinSpace;
+      </mtext>
+      <mtext>
+        &MediumSpace;
+      </mtext>
+      <mtext>
+        &MediumSpace;
+      </mtext>
+      <mtext>
+        &ThickSpace;
+      </mtext>
+      <mtext>
+        &ThickSpace;
+      </mtext>
+      <mtext>
+        &NegativeThinSpace;
+      </mtext>
+      <mtext>
+        &NegativeThinSpace;
+      </mtext>
+      <mtext>
+        &NegativeMediumSpace;
+      </mtext>
+      <mtext>
+        &NegativeThickSpace;
+      </mtext>
+      <mtext>
+        &VeryThinSpace;
+      </mtext>
+      <mtext>
+        &ThinSpace;
+      </mtext>
+      <mtext>
+        &MediumSpace;
+      </mtext>
+      <mtext>
+        &ThickSpace;
+      </mtext>
+      <mtext>
+        &NegativeVeryThinSpace;
+      </mtext>
+      <mtext>
+        &NegativeThinSpace;
+      </mtext>
+      <mtext>
+        &NegativeMediumSpace;
+      </mtext>
+      <mtext>
+        &NegativeThickSpace;
+      </mtext>
+    </mrow>
+    <annotation encoding="application/x-tex">
+      \\,\\thinspace\\:\\medspace\\;\\thickspace\\!\\negthinspace\\negmedspace\\negthickspace\\mkern1mu\\mkern3mu\\mkern4mu\\mkern5mu\\mkern-1mu\\mkern-3mu\\mkern-4mu\\mkern-5mu
+    </annotation>
+  </semantics>
+</math>
+
+`;
+
 exports[`A MathML builder tags use <mlabeledtr> 1`] = `
 
 <math>

test/mathml-spec.js

@@ -107,4 +107,15 @@ describe("A MathML builder", function() {
         expect(getMathML("\\tag{hi} x+y^2", {displayMode: true}))
             .toMatchSnapshot();
     });
+
+    it('normal spaces render normally', function() {
+        expect(getMathML("\\kern1em\\kern1ex")).toMatchSnapshot();
+    });
+    it('special spaces render specially', function() {
+        expect(getMathML(
+            "\\,\\thinspace\\:\\medspace\\;\\thickspace" +
+            "\\!\\negthinspace\\negmedspace\\negthickspace" +
+            "\\mkern1mu\\mkern3mu\\mkern4mu\\mkern5mu" +
+            "\\mkern-1mu\\mkern-3mu\\mkern-4mu\\mkern-5mu")).toMatchSnapshot();
+    });
 });